Ch. 20 Book Questions Allergy Flashcards
Which of the following is required for the sensitization of mast cells?
a. Stimulation of IgA class switching in B cells
b. One exposure to an allergen
c. Binding of antibody to high-affinity Fc receptors on the mast cell
d. Release of histamine and proteases
e. Antigen activation of TH1 cells
c. Binding of antibody to high-affinity Fc receptors on the mast cell
Sensitization of mast cells refers to the coating of mast cells with IgE (i.e., secreted IgE binding to FcɛRI receptors on the surface of mast cells). In this way, mast cells are poised for immediate activation on subsequent antigen encounter. The sequence of events in immediate hypersensitivity reactions occurs as follows: (1) first exposure to allergen; (2) antigen activation of TH2 cells and stimulation of IgE class switching in B cells; (3) production of IgE; (4) binding of IgE to FcɛRI on mast cells; (5) repeat exposure to allergen; and (6) activation of mast cells with release of mediators, such as vasoactive amines and lipid mediators in the acute phase and cytokines in the late phase.
Which one of the following is a property of mast cells but not of basophils?
a. Present next to small blood vessels in normal tissues
b. Express high levels of surface FcɛRI receptors
c. Have cytoplasmic granules containing histamine
d. Cannot proliferate as mature cells
e. Are recruited into tissues from the circulation
a. Present next to small blood vessels in normal tissues
Mast cells differ from basophils in that they are constitutively present in skin, mucosal tissues and other sites and do not circulate in blood. Mast cell progenitors in the bone marrow migrate to peripheral tissues as immature cells and undergo differentiation in situ. Mature mast cells are found throughout the body, predominantly near blood vessels and nerves and beneath epithelia; they are also present in lymphoid organs. Basophils can be thought of as the circulating counterpart of mast cells. Both mast cells and basophils express high surface levels of FcɛRI, bind IgE, and can be triggered by antigen binding to the IgE. They both contain granules with histamine and protease mediators. In contrast to mature basophils, mature mast cells retain the ability to proliferate. Only basophils are recruited into tissues from blood circulation.
Which of the following favors the development of immediate hypersensitivity?
a. TH1 responses to antigens
b. Infrequent exposure to antigens
c. Strong innate immune responses to the antigens
d. Production of interleukin-4 in response to antigens
e. Nonprotein antigens
d. Production of interleukin-4 in response to antigens
Interleukin (IL)-4 is an isotype switch factor for IgE synthesis by B cells, and IgE is essential for mast cell activation in allergic reactions. Therefore, the tendency to produce IL-4 in response to antigens, a hallmark of TH2 -type responses, favors development of immediate hypersensitivity disease. TH1 responses, which are promoted by strong innate immune responses to microbial antigens, do not favor and may actually suppress the development of immediate hypersensitivity. Allergens must be protein antigens or haptenated-protein antigens, because IgE is a T cell–dependent antibody and only proteins activate CD4+ helper T cells. In most cases, allergens are environmental antigens to which a person is repetitively exposed.
Which of the following proinflammatory mediators are preformed and stored in mast cell granules?
a. Prostaglandin D2
b. Leukotriene D4
c. Histamine
d. IL-4
e. Chemokines
c. Histamine
Mast cell granules contain various enzymes and vasoactive amines, including histamine. Prostaglandins and leukotrienes are short lived lipid mediators rapidly formed by arachidonic acid metabolism and releases upon mast cell activation. Cytokines, such as IL-4 and chemokines, are newly expressed by gene transcription upon mast cell activation and secreted.
Which of the following is a feature of bronchial asthma?
a. Hyporesponsiveness of bronchial smooth muscle cells
b. Inadequate mucus production of bronchial epithelial cells
c. No genetic predisposition for development
d. Abundant CD8+ T cells in bronchial mucosa
e. Exacerbated by viral infections
e. Exacerbated by viral infections
Asthma attacks are characterized by bronchial constriction due to smooth muscle cell hyperactivity, excessive mucus production, and abundant eosinophil and TH2 cells in the bronchial mucosa. They are frequently exacerbated by viral infections. There is a strong genetic predisposition for development of asthma and other atopic diseases.
A robust eosinophilic response is likely to be most protective in which of the following clinical scenarios?
a. A 4-year-old Brazilian child with hookworm infection
b. A 32-year-old florist with allergic rhinitis
c. A 76-year-old Chinese man with latent tuberculosis
d. A 13-year-old native of New York City with chronic asthma
e. A 58-year-old woman with community-acquired lobar pneumonia
a. A 4-year-old Brazilian child with hookworm infection
Eosinophil-mediated killing of IgE-coated helminths is an effective defense against these organisms. Thus, the activities of interleukin (IL)-4, IL-5, and IL-13 in IgE production and eosinophil activation would contribute to a coordinated defense against hookworm infection.
